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    Re: Leap seconds
    From: George Huxtable
    Date: 2009 Jan 10, 23:52 -0000

    Referring, apparently,  to posting [6933] (with which I have no
    disagreement) from Gary LaPook, GregR has written-
    Are you reading this? Because this is EXACTLY what I was referring to
    earlier (i.e. that whatever time scale we use as navigators is totally
    irrelevant - as long as we can correlate it to the time in an almanac, or
    whatever is used to obtain the date/time for a celestial event).
    I still don't know if you were being troll-ish earlier or honestly trying to
    contribute to the discussion, but at least I'm not the only one who
    understands the concept - however abstract it might be for some on the list
    to comprehend."
    Coming from anyone else on this list, I would simply laugh off the personal
    comments in that posting, but GregR has a track record of repeated and
    unwarranted personal unpleasantness in some of his earlier contributions, so
    I am disinclined to treat such matters lightly, from him.
    If he can avoid getting overheated, and deal with any question on a straight
    factual basis, as I will do, we may be able to manage fruitful discussion
    between us. Otherwise, not.
    To be honest, I'm not really sure what Greg is arguing about. He contends
    "that whatever time scale we use as navigators is totally irrelevant - as
    long as we can correlate it to the time in an almanac, or whatever is used
    to obtain the date/time for a celestial event"
    I might well agree, depending on what meaning we agree on for "correlate".
    If that includes adjusting for the number of leap seconds that would have
    occurred since the almanac was produced, which is what would need to happen
    if we adopted Atomic Time for our clocks, then GregR and I do not differ.
    I don't know how long in advance almanacs are calculated and printed, but
    let's say, for the purpose of argument, five years. So that means that the
    almanacs that we use today were produced in 2004. There was no way the
    compilers could predict, then, just how much the Earth would slow in the
    next 5 years. If we were to switch to Atomic Time, it would mean that before
    we could use any of the data in an almanac, we would need to discover how
    much the Earth's spin had diverged from its nominal rate in that interval,
    and allow for it by adjusting the reading of an accurate clock. That applies
    to predictions, not just of the Sun, but of any planet, and via GHA Aries,
    any star. Each one of us, individually, would have to work out our own
    correction, depending on the date of our almanac and the (unpredictable)
    adjustment that's called for. Instead of what happens now, when it's done
    automatically (within less than a second of error, anyway) for us all, by
    applying leap-seconds to everyone's clock.
    It's a matter of discussion whether Atomic Time or the present compromise of
    Leap-second-adjusted time is the most convenient way to work our clocks in
    the future. My personal opinion is that neither is, but a smoothly adjusted
    clock-rate, that corresponds as well as possible to the observed rotation of
    the Earth, would be more viable over the long run. But that isn't relevant
    to our present discussion.
    Let's take the chance, now, to clear up some loose ends from GregR's initial
    posting, [6805]. He had written "Besides, the almanacs have been on UT since
    when - mid 70s? (and thus pretty much "disconnected" from "sun time")."  On
    the contrary, we have seen that almanacs are, indeed, closely connected with
    Sun Time, because UT is, within less than a second, by the operation of leap
    seconds. And I have asked him what it is that he reckons occurred in the
    mid-70s to change that situation, to which there has been no reply.
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    Navigation List archive: www.fer3.com/arc
    To post, email NavList@fer3.com
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